"The argument doesn't make any sense. This is the open seat that determines a 5-4 majority on the court. It's a majority that we're very familiar with," the Oregon Democrat told MSNBC's "Morning Joe" program, referring to the 5-4 majority that Republicans had on the court until the death of Judge Antonin Scalia.

One reason Democrats are opposing Gorsuch is because Merrick Garland, President Barack Obama's choice for the seat, has not gotten his chance at the seat, and Republicans should not be allowed to "pack the court," Merkley said.

"Fighting for the integrity of the court is the right side of this battle," Merkley said.

"If you let this precedent stand, for every future vacancy, there's going to be the temptation to say, 'Hey, that seat was stolen. Let's steal the seat back.' This is a terrible, terrible moment for the way the court is viewed in America," he added.

"Picture this: You have two people confront each other. One of them pulls out a sword and says, "I've got the power. The other pulls out a machine gun and says, 'Too bad,' and then the person with the sword says, 'Well, I will just lay it down and I won't pick it up until next time I come back, and the next time you come back, the other team still has a machine gun."

Merkley on Thursday told CNN's "New Day" program that Gorsuch is "way outside the political mainstream."